Heat the oil in a large saucepan.
Add the onion, garlic, and courgettes, and fry gently for 3-4 minutes, until beginning to soften.
Add the peas and stock to the pan, bring to the boil, reduce the heat, and simmer for 5 minutes.
Season well.
Put the ingredients for the pesto in a blender and process until combined, but still retaining a slightly rough texture.